A. Field of the Invention
The present invention relates to degaussing a television receiver and in particular to preventing interference between the degaussing field and the magnetic field of the vertical yoke.
B. Related Art
Television receivers require degaussing for good beam registration on the picture tube.
The normal scheme used for degaussing includes a degaussing coil mounted at the dag of the picture tube. When the television receiver is switched "on", the degaussing coil is immediately activated and degaussing begins. The magnetic field generated by the degaussing coil is used to minimize beam registration error caused by other external magnetic fields. The total amount of time required to complete degaussing is about 350 milliseconds.
Any magnetic field present in the vertical yoke during degaussing would interfere with the magnetic field of the degaussing coil and cause error in beam registration.
European patent application EP-A 0 219 287 shows a circuit which delays turning on the V and H generator of a television receiver. In present television receivers, the V and H generator must work all the time, to increase reliability of the horizontal output transistor in the horizontal deflection circuit, regardless of whether the television receiver is on or off. Accordingly, the solution of EP-A 0 219 287 is no longer workable.
In U.S. Pat. No. 4,636,911, degaussing is attempted when the vertical deflection is near zero. However, some interference between the magnetic field of the degaussing coil and the magnetic field of the vertical yoke. Errors occurs which can result in errors in beam registration.